Limestone is calcined at ~900 °C to give CaO: CaCO3 → CaO + CO2. Metallic Ca comes from aluminothermic reduction of CaO under vacuum, or electrolysis of molten CaCl2. See calcite.
Research Elements Ca · atomic number 20 Alkaline earth metal · period 4, group 2 [Ar] 4s2 Shells: 2, 8, 8, 2 Valence electrons: 2 in the outer shell (4s2) Green dots are the outer shell's s and p electrons. Softer green dots are the d electrons of transition metals, and the d and f electrons of lanthanides and actinides: they often take part in bonding, but not always. Grey dots are the core. Ground-state configuration from the NIST Atomic Spectra Database (A. Kramida, Yu. Ralchenko, J. Reader and the NIST ASD Team). Abundance is the mole fraction of the element found as that isotope on Earth; digits in parentheses are the uncertainty in the last digits. Masses and abundances from NIST, Atomic Weights and Isotopic Compositions (J. S. Coursey, D. J. Schwab, J. J. Tsai and R. A. Dragoset, National Institute of Standards and Technology).Calcium
Electrons
How it's obtained
Natural isotopes
Isotope Relative atomic mass Abundance 40Ca 39.962590863(22) 0.96941(156) 42Ca 41.95861783(16) 0.00647(23) 43Ca 42.95876644(24) 0.00135(10) 44Ca 43.95548156(35) 0.02086(110) 46Ca 45.9536890(24) 0.00004(3) 48Ca 47.95252276(13) 0.00187(21) Compounds